A. Field of the Invention
The invention relates to facsimile systems, more particularly to a facsimile receiver.
B. Prior Art
Facsimile systems utilize a facsimile transmitter which scans a document and transmits signals representative of the contents of the document to a remote location where it is to be reproduced on a facsimile receiver. One example of a facsimile system is described in U.S. Pat. No. 3,614,319 issued Oct. 19, 1971 to Robert E. Krallinger et al and assigned to the assignee of the present invention. The system described in this patent utilizes a circular drum which rotates with respect to a "reading" head. The reading head generates signals indicative of the contents of a document which is wrapped around the drum, and it transmits these signals over a transmission medium to a remote receiver which reproduces the document. The facsimile system described in this patent produces excellent copy and is more than satisfactory for its intended purposes. However, it requires the use of an operator to load the document onto the transmitter and to unload the copy of the document from the receiver. In many cases it is desirable to provide facilities for at least the unattended reception of documents from remote locations.
In addition to the drum-type facsimile system described above, facsimile systems have also been built using a "flat-bed" scanning and reproducing system. In such a system, a document which is to be transmitted is placed on a flat table and scanned by a reading head moved across the document from side to side; the reading head is carried on a belt which rotates over pulleys. At the reproducing end, a stylus also carried by a belt moves across the paper from side to side in corresponding fashion to produce a copy of the original document. In order to avoid the "dead time" which occurs when the reading head or the stylus is returning to its starting position after scanning a line, a pair of reading heads and a pair of styli are commonly used.
Such a system imposes rather severe requirements on the reproduction process. The styli must be precisely located with respect to each other so that each starts reproduction of a line at the identical position on the paper: otherwise the beginning of the writing will vary from line to line and compromise the reproduction quality. It is difficult and expensive to maintain the necessary close tolerances in the manufacturing operation. Different wear rates of the styli or different forces pressing them against the copy paper may also cause adjacent lines to be reproduced with different optical densities, and this further compromises the reproduction quality.
An unattended receiver is especially advantageous wherever a large number of reports are to be received at a given station. For such an application however, it is necessary that the receiver paper feed and reproduction mechanism be especially free from jamming and other failures since there may be no attendant at hand to detect problems on their occurrence.